1. Field of the Invention:
The invention pertains to precision gyroscopic stable platforms for providing attitude information about three mutually perpendicular reference axes with respect to an aircraft; the invention provides a control arrangement for momentarily disabling the outer roll gimbal servo and for preventing unstable operation of the apparatus in particular flight circumstances.
2. Description of the Prior Art:
The present invention is an improvement useful in stable gyroscopic platforms of the type described in the Charles B. Reed U.S. Pat. No. 3,648,525 for a "Gyroscopic Stable Reference Apparatus", issued Mar. 14, 1972, and assigned to the Sperry Rand Corporation.
The invention of the Reed patent was devised to utilize a relatively simple construction having five gyroscopically stabilized gimbals and only one servoed gimbal, thereby rendering the stable platform relatively inexpensive, simple to manufacture, and more reliable in operation. The gimballing arrangement of the Reed device provides an all-attitude capability at the same time additionally providing accurate attitude information with respect to the three orthogonal axes of the craft on which it is mounted. By stabilizing the directional gyroscope in both pitch and roll, heading information is provided generally free from the gimbal errors of a conventionally mounted directional gyroscope. However, one difficulty remains indentifiable in the Reed device, since under certain conditions of operation in an aircraft, the outer roll servo loop of the instrument can become unstable and the outer roll gimbal may thereupon oscillate or even spin about its axis, destroying the validity of the navigation output information of the instrument.